Cut-off Machine Report

Abrasive Cut-Off Machine Report and the Detail Design of the Cut-Off Machine

MOW 217 Benade DJ 26317088 Kraamwinkel FH 26209382 Van Staden HJ 26059802

Table of Content List of Tables......................................................................................................3 List of Figures.....................................................................................................4 List of Symbols...................................................................................................5 1. Introduction....................................................................................................6 2. User Requirements.........................................................................................7 3. Literature Study..............................................................................................7 4. Functional Analysis.........................................................................................8 4.1 System Level.............................................................................................8 4.2 Mission Level.............................................................................................8 4.3 System Level Functional Diagram.............................................................9 4.4 First Level Functional Diagram..................................................................9 4.5 Design Parameters per Function.............................................................10 5. Design Specifications...................................................................................11 6. Concepts & Concept Evaluation...................................................................12 7. Design calculations.......................................................................................15 7.1 Power Transmission and Torque..............................................................15 7.2 Forces on Pulley......................................................................................16 7.3 Shear Force and Bending Moment..........................................................16 7.4 Safety Factor of Shaft (Dynamic)............................................................18 7.5 Safety Factor of Shaft (Fatigue)...............................................................19 7.6 Bearing Calculations................................................................................20 7.7 Pulley Design...........................................................................................22 8. Detail Design................................................................................................22 8. Detail Design

List of Tables

List of Figures Figure 5.1 Schematic Drawing for the cut-off machine layout.............................12 Figure 5.2 Forces on cutting disc and pulley.......................................................12 Figure 5.2 Forces on the cutting disc and pulley.

List of Symbols Symbol

Unit

Angular Velocity

ω

rad/s

Axial load

Fa

N

Basic life rating

L10

106 cycles

Bending moment at Q

MQ

Nm

Bending moment at R

MR

Nm

Diameter d

d

mm

Diameter D

D

mm

Dynamic load

P

N

Dynamic load rating

C

KN

Endurance limit

Se

Mpa

Force in v-belt (slack side)

FB1

N

Force in v-belt (Taut side)

FB2

N

Force on cutting disc

FC

N

Load factor

kc

Maximum normal stress

σmax

Mpa

Maximum shear stress

τmax

Mpa

Miscellaneous factor

kf

Moment

M

Nm

Moment of inertia

I

m4

Normal stress

σ

Mpa

Power input to the arbor shaft

Pin

W

Power output from motor

Pout

W

Radial load

Fr

N

Radius r

r

mm

Reaction force on Q in the y-direction

Qy

N

Reaction force on Q in the z-direction

Qz

N

Reaction force on R in the y-direction

Ry

N

Reaction force on R in the z-direction

Rz

Reliability factor

ke

Rotational speed

n

Safety factor

FS

N

Rpm

J

m4

Shear force between P and Q

VPQ

N

Shear force between Q and R

VQR

N

Shear force between R and S

VRS

N

Second moment of inertia

Shear stress

τ

Mpa

Size factor

kb

Static load

Po

N

Static load rating

C0

KN

Surface factor

ka

Temperature factor

kd

Torque

T

Nm

Ultimate tensile strength

Su

Mpa

Yielding strength

Sy

Mpa

1. Introduction A cut-off is one of the most commonly used machinery in the manufacturing process, and almost every workshop has one. It is easy to use, maintainable and cost effective. The task was given to a group of engineers in training to design an abrasive cut-off machine for cutting steel. After considering a few concepts, along with a literature study, the final design and calculations were done. Included in the final design are a modelled CAD drawing with detail drawings.

2. User Requirements An abrasive cut-off machine has to completely designed for cutting steel. It must be able to cut 50mm solid steel and 75mm steel pipes. The cut-off machine should be fitted with safety guards where required and also have an adjustable down stop to the limit the depth of the cut. A mechanism is required for pulling the machine down when someone is cutting.

3. Literature Study

4. Functional Analysis 4.1 System Level

Abrasive Cut -Off Machine

Cutting Steel

Up to 50mm solid steel

Ø304mm cutting Disc

Up to 75mm steel pipe

4.2 Mission Level

• • •

Long live expectancy Maintainable Reliable

Electric Motor

5 HP

Adjustable down stop

• • • • •

Functional Simplicity Safety Productivity Easy to use

4.3 System Level Functional Diagram Start Motor 1.1

Pulling Down Machine 1.2

Cut Steel 1.0

Cutting 1.3

Pulling Up the Machine 1.4

Stop Motor 1.5

4.4 First Level Functional Diagram

Cut-off Machine Functional 2.0

Start Motor 1.1

Pull Down 1.2

Is cutting disc clear of work peace 1.1.1

Yes

Pull down on handle 1.2.1

Press Start Button 1.1.2

Pull Down 1.2

Pull machine up using handle 1.1.3

Press Start Button 1.1.4

Cutting 1.3

Finished cutting 1.2.2

Yes

Pull Up 1.4

No

Cutting 1.3

Pull machine down using handle 1.3.1

Pull Up 1.4

Pull down on handle 1.4.1

Press Stop Button 1.4.2

Motor Stop 1.5

Remove Work peace 1.5.1

4.5 Design Parameters per Function 1.1.Start Motor 1.1.1.Is cutting disc clear of work peace 1.1.2.Press button 1.1.3.Pull up 1.1.4.Press button

1.2.Pull Down 1.2.1.Pull handle

1.2.2.Finished cutting 1.3.Cutting 1.3.1.Hold handle down

1.4.Pull Up 1.4.1.Press stop button 1.4.2.Remove work piece

Start button visible Start button reachable Use handle Start button visible Start button reachable

Handle long enough Hand grip (ergonomics) Enough momentum Desired cut achieved

Handle long enough Sparks directed backwards Pulley and disc safety guard Cutting machine staionary Button visible Red Release clamp

1.5.Motor Stop

5. Design Specifications Basic specifications for abrasive cut-off machine Symbol Cutting wheel capacity

Value

Unit

Ø 304

mm

Cutting wheel speed

nshaft

4000

rpm

Motor (Single Phase)

Pout

3.75

kW

Motor Speed

nmotor

2950

rpm

Hole in Cutting Disc

d

Ø25

mm

Use EN3 steel for shaft

Sy

325

MPa

Su

450

MPa

Symbol

Value

Unit

No power losses in pulley drive

η

1

-

Operating temperature

T

60

°C

Mass of shafts and pulley are neglable

m

0

kg

Tabel 5.1 Basic specifications for abrasive cut-off machine

Assumptions

Tabel 5.2 Assumptions

Figure 5.1 Schematic drawing for the cut-off machine layout

Figure 5.2 Forces on the cutting disc and pulley.

6. Concepts & Concept Evaluation Concept 1

Figure 6.1 Concept 1

In the concept the hinge point is situated at the rear of the machine. Pulleys with V-belts will be used to transmit power from the motor to the arbor shaft.

Concept 2

Figure 6.2 Concept 2

In this concept the hinge is located slightly in front of the motor (if the cutting disc is said to be the front), this will act like a “see-saw”. When the machine is not busy cutting steel, the cutting disc will be kept in the air due to the weight of the motor at the back. Pulleys and a V-belt will be used for power transmission.

Concept 3

Figure 6.3 Concept 3

Fixing the cutting disc to the motor shaft directly.

Concept 4

Figure 6.4 Concept 4

The motor will be mounted on a steel plate and the cutting disc mounted on the motor shaft. The plate with the motor will be able to slide between two slots to keep it steady while the motor is pulled up with a chain and pulley or moving down because of the motors weight (and gravity).

Concept Evaluation Concept 1

Concept 2

Concept 3

Concept 4

Simplicity

4

4

4

2

Practicability

3

5

2

2

Manufacturability

4

4

5

3

Maintainability

4

4

5

3

Yielding Possibility

4

4

2

2

Safety

3

4

1

1

Cost

3

3

5

2

Able to comply with specs Total

5

5

1

1

30

33

25

16

Table 6.1 Concept Evaluation

Thus from the evaluation, Concept 2 will be the best option.

7. Design calculations 7.1 Power Transmission and Torque.

Power on shaft Toque on shaft

Pout = ηPin T = (60P)/(2πn)

P T

3750 W 8.95 Nm

Assume η =1

7.2 Forces on Pulley

FB1

221 N

FB2

400 N

Ød

100 mm

T

8.95 Nm

ØD C

T

300 mm 59.67 N 8.95 Nm

7.3 Shear Force and Bending Moment

Qy

322.38 N

Ry

883.68 N

Qz

450 N

Rz

150 N

Moment at Q

MQ

30.588 Nm

Moment at R

MR

46.575 Nm

Shear Force between P & Q Shear Force between Q & R Shear Force between R & S

VPQ

305.877 N

VQR

302.517 N

VRS

621 N

7.4 Safety Factor of Shaft (Dynamic)

M T d

46.575Nm 8.95Nm 0.025m

Steel

Sy

325MPa

Su

450MPa

Te=(M2+T2)1/2

τ=16Te/πd

3

τmax= Sy/2FS

Te

47.4271 3Nm

τ

154588 56Pa

FS

10.5117 7

7.5 Safety Factor of Shaft (Fatigue)

From SKF Ød ØD r

6305 25mm 32mm 1mm

M T Steel

46.575Nm 8.95Nm

Sy

325MPa

Su

450MPa

Endurance Limit Se’= 0.5Sut

Se’

Surface Factor

ka = 4.51 Sut-0.265

ka

0.893

Size Factor

kb=1.24d-0.107

kb

0.879

kc

1

Load Factor

kd

Temp Effects Reliability Miscellaneous factor Se = kakbkckdkekfS’e

225 Mpa

1

ke

0.897

kf

1

Se

158.45 Mpa

Sut ≤ 1460 MPa Machined 2.79 ≤ d ≤ 51 mm Combined Loading T< 300°C 90% Reliability No Corrosion

Stress Concentration D/d

1.28

r/d

0.04

Bending Table A-13-9 (Shigley) Fig 6.20 (Shigley) Kf = 1 + q(Kt – 1)

Kt

2.1

q

0.7

Kf

1.77

Kts

1.7

Torsion Table A-13-8 (Shigley) Fig 6.21 (Shigley) Kfs = 1 + qs(Kts – 1)

qs Kfs

0.85 1.595

Alternating and mean stresses σ a = 32M/πd3

σa

30.36 MPa

σm= 0

σm

0.00 MPa

τa

0.00 MPa

τm

2.92 MPa

σ a’

53.74 MPa

τa = 0 τm = 16T/πd

3

Combine Components: Tresca σ a’ = ((kf σa)2 + 3(kfsτa)2)1/2 σm’ = ((kf σm)2 + 3(kfsτm)2)1/2 Mean Stress: Asme (nσ’a/Se)2 + (nσ’m/Sy)2 = 1

σm’

n

9.31 MPa

2.94 → FS

7.6 Bearing Calculations y-component at Q

Qy

322.38 N

z-component at Q Resultant force at Q y-component at R z-component at R Resultant force at R

Q=(Qy2+QZ2)1/2

R=(Ry2+RZ2)1/2

Qz

450.00 N

Q

553.56 N

Ry

883.68 N

Rz

150.00 N

R

896.32 N

Radial force on bearing Axial force on bearing

Fa

Design Temp Rotational Speed

T n

Design for L10h = (C/P)p x (106/60n) →

Fr

896.32 N 0.00 N 60 °C 4000.00 rpm

L10h

25000.0 0 hours

C

16.29 kN

Choose SKF 6305 Explorer Roller Bearing From SKF

C

23.40 kN

C0 d D

11.60 kN 25.00 mm 62.00 mm

Equivalent dynamic bearing load FA /FR P = FR

0.00 N P

896.32 N

Po = 0.6Fr + 0.5Fa

P0

537.79 N

P0 < FR → P0 = FR

P0

896.32 N

Equivalent static bearing load

Static Safety Factor

S0 = C0/P0

S0

12.94 is > 1

Basic Rating Life L10 = (C/P)p L10h = L10x (106/60n)

(p=3 for roller bearings)

L10 L10h

17793.3 5 Cycles 74138.9 5 hours

Adjusted Rating Life SKF table 1 p53

a1

dm=0.5(d+D) SKF diagram 5 p60 SKF diagram 6 p61

dm v1

v ĸ = v/v1 SKF Diagram 1 p54

ĸ a23

Lna = a1a23L10

Lna

7.7 Pulley Design

Speed Ratio n 1d1 = n 2d2

d2 Round d2

135.59mm 136.00mm

1.00

90% Reliability

43.50 mm at dm and 4000 10.00 mm2/s rpm ISO VG 22 at 60°C an d v1 24.00 mm2/s at 40°C 2.40 2.00 35586.7 0 hours

at ĸ = 2.4 Which is sufficient

Power Transmission T = (FB2 – FB1)xd/2

T

8.95Nm

Fi

89.5N

Pre-tension Fi = (FB2 – FB1)/2 Fc

8. Detail Design

9. Conclusion

10. References

11. Annexure 11.1 Appendix A